Cleaned the interrupt code a bit

src/interrupts.c

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2022 Dominic Masters
+ * 
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "interrupts.h"
+
+void interruptOnScanline() {
+  if(LYC_REG == 0) {
+    LCDC_REG |= LCDCF_BG8000;
+    if((TEXTBOX_STATE & TEXTBOX_STATE_VISIBLE) != 0) {
+      LYC_REG = INTERRUPT_TEXTBOX_VRAM;
+    }
+  } else if(LYC_REG == INTERRUPT_TEXTBOX_VRAM) {
+    LCDC_REG &= ~LCDCF_BG8000;
+    LYC_REG = 0;
+  }
+}